Stacked III-V semiconductor diode

ABSTRACT

A stacked III-V semiconductor diode comprising or consisting of GaAs with a highly n-doped cathode layer, a highly p-doped anode layer and a drift region arranged between the cathode layer and the anode layer, wherein the drift region has a low n-doped drift layer and a low p-doped drift layer, the n-doped drift layer is arranged between the p-doped drift layer and the cathode layer, both drift layers each have a layer thickness of at least 5 μm and, along the respective layer thickness, have a dopant concentration maximum of not more than 8·1015 cm−3, the dopant concentration maxima of the two drift layers have a ratio of 0.1 to 10 to each other and a ratio of the layer thickness of the n-doped drift layer to the layer thickness of the p-doped drift layer is between 0.5 and 3.

This nonprovisional application claims priority under 35 U.S.C. § 119(a)to German Patent Application No. 10 2021 000 609.7, which was filed inGermany on Feb. 8, 2021, and which is herein incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a stacked III-V semiconductor diodecomprising or consisting of GaAs, having a highly n-doped cathode layer,a highly p-doped anode layer and a drift region arranged between thecathode layer and the anode layer.

Description of the Background Art

A high-voltage resistant semiconductor diode with a p+-n-n+ structuremade of gallium arsenide is known from “GaAs Power Devices” by GermanAshkinazi, ISBN 965-7094-19-4, pages 8 and 9.

Further stacked III-V semiconductor diodes are known from EP 3 321 971B1, which corresponds to US 2018/0138320, and from EP 3 321 970 B1,which corresponds to US 2018/138043, which are all herein incorporatedby reference, wherein the semiconductor diodes have an additionalintermediate layer between the drift region and the cathode or anode.

Further semiconductor devices are known from DE 10 2016 111 844 A1(which corresponds to US 2017/0373157), JP H06-314 801A and DE 10 2018000 395 A1 (which corresponds to US 2019/0221676 and is incorporatedherein by reference).

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a devicethat further develops the prior art.

In an exemplary embodiment of the invention, a stacked III-Vsemiconductor diode is provided comprising or consisting of GaAs, havinga highly n-doped cathode layer, a highly p-doped anode layer and a driftregion arranged between the cathode layer and the anode layer.

The drift region has a low n-doped drift layer and a low p-doped driftlayer, wherein the n-doped drift layer is arranged between the p-dopeddrift layer and the cathode layer.

Both drift layers each have a layer thickness of at least 5 μm and,along the respective layer thickness, a dopant concentration maximum ofnot more than 8·10¹⁵ cm⁻³.

The dopant concentration maxima of the two drift layers to each otherhave a ratio of 0.1 to 10.

The ratio of the layer thickness of the n-doped drift layer to the layerthickness of the p-doped drift layer is between 0.5 and 3.

It is understood that all semiconductor layers of a semiconductor diodeconsisting of GaAs or comprising GaAs, in particular the cathode layer,the anode layer and the drift region, each consist of GaAs or at leastcomprise GaAs.

In other words, each semiconductor layer of the III-V semiconductordiode has at least the elements Ga and As.

The semiconductor layers can be produced by epitaxy. In a furtherdevelopment, the cathode layer or the anode layer can be formed by asubstrate layer. Preferably, further III-V semiconductor layers areepitaxially grown on the substrate layer to form the III-V semiconductordiode.

Alternatively, the III-V semiconductor diode comprises at least onesemiconductor bond. Here, surfaces of two GaAs semiconductor discs orGaAs wafers are joined together.

The doping of the respective GaAs semiconductor layers can be introducedduring epitaxy. Preferably, epitaxy is performed by means of MOVPEand/or LPE.

Doping can also be carried out by means of ion implantation afterepitaxial growth or, alternatively, instead of being introduced duringepitaxy.

In addition, the semiconductor diode can have further layers of othermaterials, in particular metallic connection contact layers. Theconnection contact layers are formed, for example, completely orpartially of a metal, e.g., gold, or of a metal alloy and are generated,for example, by electron beam evaporation or by sputtering.

At least the area of the cathode layer and the anode layer adjacent to aconnection contact layer preferably has a high dopant concentration inorder to form the lowest possible low impedance contact and to keep theseries resistance or the power dissipation of the semiconductor diode aslow as possible.

The drift region is characterized by a total width of at least 10 μm.The total width can be at least 20 μm or at least 40 μm or at least 60μm. The total width is divided into a weakly p-doped and a weaklyn-doped region or layer.

The ratio of the layer thicknesses of the two drift layers is chosensuch that the n-doped drift layer is at least half as thick as thep-doped drift layer or that the n-doped drift layer is at most threetimes as thick as the p-doped drift layer.

The respective dopant concentration of the two drift layers is as low aspossible in a region adjacent to the other drift layer and, ifnecessary, ascends slightly in a direction pointing away from the otherdrift layer. In a further development, the ascension occurs in one ormore steps.

The p-n junction thus forms within the drift region and in an area withvery low dopant concentrations.

Due to the wide drift region formed of two differently low doped layers,diodes with particularly high reverse voltages of over 1100 V or evenover 1200 V can be achieved and produced with small switch-on resistorsand particularly low capacitances per area.

In a further development, isoelectric or isovalent centers areincorporated into the p-doped drift layer and/or the anode layer inorder to increase the switching speed, i.e., the change between backwardand forward direction. Here, the isoelectric or isovalent centersrepresent impurity complexes. The impurity complexes are energeticallydeep-lying and significantly reduce the charge carrier life, i.e., thecenters empty the charge carriers, especially in reverse operation.

In one embodiment, the isoelectric centers include N and/or Zn-0 and/orMn and/or an element from the III and/or an element from the V maingroup.

In another further development, the concentration of the isoelectriccenters is in a range between 5·10¹¹ cm⁻³ and 8·10¹⁴ cm⁻³ or in a rangebetween 5·10¹² cm⁻³ and 1·10¹⁴ cm⁻³ or in a range between 1·10¹³ cm⁻³and 8·10¹³ cm⁻³. Preferably, the concentration of the isoelectriccenters is below the dopant concentration of the respective area of thedrift layer or the anode layer by a factor of 1000 up to a factor of 10or by a factor of 100 up to a factor of 20.

In particular, GaAs power diodes can be produced with a reverse recoverycharge of no more than 80 nC per 1 mm diode area.

The layer thickness of the n-doped drift layer can be greater than thelayer thickness of the p-doped drift layer. The n-doped drift layerand/or the p-doped drift layer can have a layer thickness of at least 20μm or at least 40 μm. The particularly high layer thickness of bothdrift layers makes it possible in particular to improve the dielectricstrength of the diode.

The n-doped drift layer can have an ascending dopant concentration curvealong the layer thickness in the direction of the cathode layer up tothe dopant concentration maximum.

The slow reduction of the dopant concentration of the n-doped driftlayer in the direction of the p-doped drift layer makes it possible inparticular to achieve very low dopant concentrations and to produce acontrolled and reproducible p-n transition.

The p-doped drift layer can have an ascending dopant concentration curvealong the layer thickness in the direction of the anode layer up to thedopant concentration maximum. As already explained, the ascension canalso occur in a step-like curve.

The ascending dopant concentration curve is linear or concave or convex.For example, a convex rise follows a Gauss curve, a concave rise followsan exponential function, for example. It is understood that theconcentration curve is always less than the maximum doping of 8·10¹⁵cm⁻³.

The dopant concentration curve of the n-doped drift layer and/or thep-doped drift layer can have one or more steps along the layerthickness. One or more steps or each step has a convex flank or aconcave flank or a linear flank in alternative further developments.

The dopant concentration curve of the two drift layers may each drop inthe direction of the other drift layer to a value less than 3·10¹⁵ cm⁻³or less than 6·10¹⁴ cm⁻³ or less than 3·10¹⁴ cm⁻³ or less than 2·10¹⁴cm⁻³.

The dopant concentration along at least 80% thickness of the n-dopeddrift layer and/or the p-doped drift layer can be greater than 5·10¹³cm⁻³.

The cathode layer can have a dopant concentration of at least 1·10¹⁸cm⁻³ or at least 5·10¹⁸ cm⁻³ or at least 8·10¹⁸ cm⁻³.

The anode layer can have a dopant concentration of at least 1·10¹⁷ cm⁻³or at least 5·10¹⁷ cm⁻³ or at least 8·10¹⁸ cm⁻³. The low doping makes itpossible to improve the switch-off behavior of the diode and to reducethe recovery charge.

It is understood that in particular in an area of the cathode and anodelayer adjacent to the metallic connection contacts, the highest possibledopant concentration is sought in order to keep the series resistance ofthe diode as low as possible or to establish a low impedance contact.

The cathode layer and/or the anode layer can have a layer thickness ofat least 2 μm or at least 5 μm or at least 20 μm. A low layer thicknessmade it easier to keep the series resistance of the diode low.

The cathode layer and/or the anode layer can comprise a first sectionwith a constant dopant concentration curve and a second section arrangedbetween the first section and the drift region with a dopantconcentration curve which ascends in a linear and/or concave and/orstep-like manner in the direction of the first section. Preferably, thestepped dopant concentration area comprises or consists of one step ortwo steps or three steps.

In particular, the second layer section makes it possible to shape thetransition of the dopant concentration from the low level in the area ofthe drift region to a significantly higher level of the second sectionof the anode and/or cathode layer.

The second layer section can have at least one step or has exactly onestep or has at least two or has exactly two steps in the curve of thedoping profile.

In a single step at the top of said step, the dopant concentration canbe greater than the factor 2 or greater than the factor 5 or greaterthan the factor 8 than the dopant concentration of the drift layeradjacent to the second region.

By avoiding a sudden transition, i.e., an increase in the dopantconcentration of 8·10¹⁵ cm⁻³ to the dopant concentration of the firstsection, by means of a gradual or incremental ascension over atransition area, i.e., the second section, the switch-off behavior ofthe diode is significantly improved.

The second section can have a layer thickness of at least 0.5 μm and atmost 10 μm. Preferably, the second section of the cathode layer has alayer thickness of 3 μm to 5 μm, whereas the second section of the anodelayer preferably has a layer thickness of 2 μm to 4 μm.

The cathode layer or the anode layer can be formed as a substrate.Typical layer thicknesses of an anode or cathode layer formed as asubstrate are 100 μm to 250 μm.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes, combinations,and modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art from this detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are not limitiveof the present invention, and wherein:

FIG. 1 is a view of an example of a stacked III-V semiconductor diode,

FIG. 2 is a view of an example of the stacked III-V semiconductor diode,

FIG. 3 is a view of an example of the stacked III-V semiconductor diode,

FIG. 4 is a dopant concentration curve along the stacked III-Vsemiconductor diode in a further embodiment, and

FIG. 5 is an example of the dopant concentration curve along the stackedII-V semiconductor diode.

DETAILED DESCRIPTION

The illustration of FIG. 1 shows a view of a first embodiment of astacked III-V semiconductor diode 10 comprising GaAs or consisting ofGaAs. A highly n-doped substrate layer forms a cathode layer 12, onwhich the drift region 14 is arranged with a total thickness D_(D),followed by a highly p-doped anode layer 16 with a layer thicknessD_(A).

The drift region 14 is divided into a weakly n-doped drift layer 14.1with a layer thickness D_(n) adjacent to the cathode layer 12 and aweakly p-doped drift layer 14.2 with a layer thickness D_(p) arrangedbetween the n-doped drift layer 14.1 and the anode layer 16.

The cathode layer 12 formed by a substrate accordingly has a slightlygreater layer thickness DK of 50 μm to 250 μm. A dopant concentration ofthe cathode layer is preferably at least 8·10¹⁸ cm⁻³ and is constant orat least substantially constant along the layer thickness.

The other layers are preferably epitaxially produced on the cathodelayer 12. The doping can be generated during epitaxy or subsequently byion implantation. The layer thickness D_(n) of the n-doped drift layer14.1 is at least 5 μm, preferably at least 40 μm. A dopant concentrationdrops from a dopant concentration maximum of not more than 8·10¹⁵ cm⁻³,preferably from a maximum of 2·10¹⁵ cm⁻³, in the direction of thep-doped drift layer 14.2.

The layer thickness D_(p) of the p-doped drift layer 14.2 is at least 5μm, preferably at least 20 μm. Preferably, the layer thickness D_(p) ofthe p-doped drift layer 14.2 is half or one third of the layer thicknessD_(n) of the n-doped drift layer 14.1. A dopant concentration of thep-doped drift layer 14.2 increases in the direction of the anode layer16 up to a dopant concentration maximum of at least 1·10¹⁷ cm⁻³ or atleast 1·10¹⁸ cm⁻³.

In the illustration of FIG. 2 , another embodiment is shown. In thefollowing, only the differences to the illustration in FIG. 1 areexplained.

The stacked III-V semiconductor diode 10 has a cathode layer 12 with afirst section 12.1 having a constant dopant concentration of at least1·10¹⁸ cm⁻³, preferably of at least 8·10¹⁸ cm⁻³ and with a secondsection 12.2. The second section 12.2 is arranged between the firstsection 12.1 and the drift region 14 and has a relatively low layerthickness D_(K2) of 0.5 μm to 10 μm, preferably from 3 μm to 5 μm.

The second layer section serves to shape the transition of the dopantconcentration from the highly doped first section 12.1 of the cathodelayer to the low n-doped drift layer 14.1. The second section 12.2 hasfor this purpose a dopant concentration curve ascending in the directionof the first section 12.1 from a dopant concentration minimum to adopant concentration maximum. The dopant concentration curve is linearor concave or convex or stepped with one step or with several steps. Ina step-like curve, the flank of one or more steps or of all steps ispreferably convex or concave or linearly formed.

In an example, the dopant concentration maximum of the second section12.2 corresponds to the dopant concentration of the first section 12.1,while the dopant concentration minimum of the second section 12.2corresponds to the dopant concentration maximum of the n-doped driftregion. In other embodiments, a jump in the dopant concentration isformed at the interface between the first and second sections 12.1, 12.2and/or between the second section 12.2 and the drift region 14, whereinthe jump in the dopant concentration, due to the dopant concentrationcurve of the second section 12.2, is lower than in an embodiment of thesemiconductor diode 10 without the second cathode section 12.2.

In the illustration of FIG. 3 , another example is shown. In thefollowing, only the differences to FIG. 2 are explained.

The stacked III-V semiconductor diode 10 has an anode layer 16 with afirst section 16.1 with a constant dopant concentration of at least1·10¹⁷ cm⁻³ and a second section 16.2 with a dopant concentrationprofile ascending in the direction of the first section 16.1 and a layerthickness D_(A2) from 0.5 μm to 10 μm, preferably from 2 μm to 4 μm.

Like the second section 12.2 of the cathode layer 12, the second section16.2 of the anode layer 16 serves to shape the transition of the dopantconcentration. The dopant concentration curve of the second section 16.2is linear or concave or convex or stepped with one or more steps. In astep-like curve, the flank of one or more steps or of all steps ispreferably convex or concave or linearly formed.

The stacked III-V semiconductor diode 10 can have the anode layer 16with the two sections 16.1 and 16.2 and a drift layer 14 described abovein the first embodiment of FIG. 1 , i.e., without the second section12.2.

In the illustration of FIG. 4 , another example is shown. In thefollowing, only the differences to FIG. 1 are explained.

FIG. 4 shows various dopant concentration curves along the stacked III-Vsemiconductor diode 10 with a layer sequence corresponding to theembodiment of FIG. 1 . In alternative embodiments, the dopantconcentration curve of the n-doped drift layer 14.1 proceeds convex orconcave or linearly ascending in the direction of the cathode layer 12.

The dopant concentration curve of the p-doped drift layer 14.2 proceedsin the direction of the anode layer 16 in a constant or ascendingmanner, wherein the ascension is stepped or convex or linear or concave.

The convex rise of the n-doped and/or the p-doped drift layer 14.1 or14.2 is gauss-shaped.

Alternatively, in an embodiment the concave ascension of the n-dopedand/or the p-doped drift layer 14.1 or 14.2 follows an exponentialcurve.

In the illustration of FIG. 5 , another example is shown. In thefollowing, only the differences to the illustration of FIG. 3 areexplained.

In FIG. 5 , various dopant concentration curves along the stacked III-Vsemiconductor diode 10 are shown as examples.

The dopant concentration curve begins with a constant, high dopantconcentration of n-dopants over the first section 12.1 of the cathodelayer 12, followed by a dopant concentration drop over the secondsection 12.2 of the cathode layer, wherein the drop is convex and beginsat the dopant concentration level of the first section 12.2 or at asignificantly lower level.

Subsequently, the dopant concentration drops further over the n-dopeddrift layer 14.1. The drop takes place more slowly and with or withoutsteps.

Between the n-doped drift layer 14.1 and the p-doped drift layer 14.2, achange of the dopant takes place, wherein the p-doped drift layer 14.2in the embodiment shown has a constant or linearly ascending or steppedconcentration of p-dopants.

In the second section 16.2 of the anode layer 16 adjacent to the driftregion, the dopant concentration of p-dopants ascends in a step-likemanner over several rectangular steps. The subsequent first section 16.1of the anode layer 16 has a constant dopant concentration level of atleast 1·10¹⁷ cm⁻³.

In addition, the anode layer 16 has a third section 16.3 following thefirst section 16.1, so that the first section 16.1 is arranged betweenthe second section 16.2 and the third section 16.3. The third section16.3 has a higher dopant concentration than the first section 16.1,preferably a constant dopant concentration of at least 5·10¹⁸ cm⁻³ or ofat least 1·10¹⁹ cm⁻³.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are to beincluded within the scope of the following claims.

What is claimed is:
 1. A stacked III-V semiconductor diode comprising orconsisting of GaAs, and comprising: a highly n-doped cathode layer; ahighly p-doped anode layer; and a drift region arranged between thecathode layer and the anode layer, the drift region having a low n-dopeddrift layer and a low p-doped drift layer, wherein the n-doped driftlayer is arranged between the p-doped drift layer and the cathode layer,wherein both drift layers each have a layer thickness of at least 5 μmand, along the respective layer thickness, a dopant concentrationmaximum of not more than 8·10¹⁵ cm^(−3,) wherein the dopantconcentration maxima of the two drift layers to each other have a ratioof 0.1 to 10, wherein a ratio of the layer thickness of the n-dopeddrift layer to the layer thickness of the p-doped drift layer is between0.5 to 3, and wherein the anode layer and/or the cathode layer has afirst section with a constant dopant concentration curve and a secondsection arranged between the first section and the drift region with adopant concentration curve ascending in a step-like manner in thedirection of the first section.
 2. The stacked Ill-V semiconductor diodeaccording to claim 1, wherein the layer thickness of the n-doped driftlayer is greater than the layer thickness of the p-doped drift layer. 3.The stacked III-V semiconductor diode according to claim 1, wherein then-doped drift layer and/or the p-doped drift layer has a layer thicknessof at least 20 μm or at least 40 μm.
 4. The stacked III-V semiconductordiode according to claim 1, wherein the n-doped drift layer has anascending dopant concentration curve along the layer thickness in thedirection of the cathode layer up to the dopant concentration maximum.5. The stacked III-V semiconductor diode according to claim 1, whereinthe p-doped drift layer has an ascending dopant concentration curvealong the layer thickness in the direction of the anode layer up to thedopant concentration maximum.
 6. The stacked III-V semiconductor diodeaccording to claim 4, wherein the ascending dopant concentration curveis linear or concave or convex or comprises a plurality of steps.
 7. Thestacked III-V semiconductor diode according to claim 4, wherein thedopant concentration curve of the n-doped drift layer and/or the p-dopeddrift layer has one or more steps along the layer thickness.
 8. Thestacked III-V semiconductor diode according to claim 7, wherein one stepor several steps or each step has a convex flank or a concave flank or alinear flank.
 9. The stacked Ill-V semiconductor diode according toclaim 4, wherein the dopant concentration curve of the two drift layersin the direction of the other drift layer drop to a value less than9·10¹⁴ cm⁻³ or less than 6·10¹⁴ cm⁻³ or less than 3·10¹⁴ cm⁻³ or lessthan 2·10¹⁴ cm⁻³.
 10. The stacked III-V semiconductor diode according toclaim 1, wherein the cathode layer and/or the anode layer has a dopantconcentration of at least 1·10¹⁷ cm⁻³ or at least 5·10¹⁸ cm⁻³ or atleast 8·10¹⁸ cm⁻³.
 11. The stacked III-V semiconductor diode accordingto claim 1, wherein the cathode layer and/or the anode layer has a layerthickness of at least 2 μm or at least 5 μm or at least 20 μm.
 12. Thestacked III-V semiconductor diode according to claim 1, wherein thecathode layer has a first section with a constant dopant concentrationcurve and a second section arranged between the first section and thedrift region with a dopant concentration curve ascending in a linearand/or concave and/or step-like manner in the direction of the firstsection.
 13. The stacked III-V semiconductor diode according to claim 12wherein the second section has a layer thickness of at least 0.5 μm andof a maximum of 10 μm of at least 2 μm and at most 4 μm.
 14. The stackedIII-V semiconductor diode according to claim 1, wherein the cathodelayer or the anode layer is formed as a substrate.
 15. The stacked Ill-Vsemiconductor diode according to claim 1, wherein the p-doped driftlayer and/or the anode layer have isoelectric or isovalent centers toincrease the switching speed.